Another Option for Missing “Sign in as Different User” link in SharePoint 2013
In SharePoint 2010, there was a wonderful option called “Sign in as Different User” that would allow you to quickly, easily and painlessly switch user accounts in the browser without losing your place on a site. This worked wonderfully for developers and for Admins where they have multiple IDs. However, it confused the average user and generated support calls because it would break other Office functionality so Microsoft removed it from the interface. They did not remove the functionality from SharePoint though it is entirely possible (read: likely) that they will do so in the next version.
Microsoft has documented a few relatively simple ways around this but I was looking for something a little faster and that was as easy as it was in SharePoint 2010. To that end, I took the second option in their recommendation and tweaked it a little bit.
This solution is intended for developers and administrators only as they generally have the technical depth to understand the ramifications of processes running under different IDs. If you need a solution to this for your whole user base, then you will need to look at the third option in Microsoft’s note above.
This walks through the same logout/login mechanism that was in SharePoint 2010 and, best of all, bounces you right back to the page you were on but now as the new user identity. It is even one click faster than the same process in 2010 :)